This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-115379, filed Apr. 17, 2000, the entire contents of which are incorporated herein by reference.
This invention relates to an exhaust gas cooling system.
The exhaust gas to be emitted from the combustion in a boiler, etc. incorporated in a power-generating installation such as a thermal power plant for instance contains a large quantity of carbon dioxide. This carbon dioxide is known to bring about a green house effect causing a global warm-up phenomenon, and hence researches for the countermeasure to the generation of carbon dioxide is an urgent problem internationally at present in view of preserving the global environment. Under the circumstances, a method of removing and recovering carbon dioxide from exhaust gas by contacting the exhaust gas with an absorbent such as an aqueous solution of alkanolamine as well as a method of reserving the carbon dioxide thus recovered without allowing carbon dioxide to be released into air atmosphere are intensively studied.
However, since the exhaust gas generated from the combustion in a boiler is high in temperature (for example, about 190xc2x0 C.), it is impossible to directly contact the exhaust gas with the aforementioned aqueous solution of alkanolamine. Therefore, the absorption and recovery of the exhaust gas is now precooled to about 40xc2x0 C. before the exhaust gas is introduced into the aqueous solution of alkanolamine.
In the meantime, there is known an apparatus shown in FIG. 5 as a cooling system for cooling the exhaust gas. Namely, according to this cooling system of exhaust gas, an exhaust gas-processing tower 103 has an exhaust gas inlet port 101 at a lower portion thereof and an exhaust gas outlet pipe 102 at an upper portion thereof. A spray member 104 for spraying cooled water is provided at an upper portion of the interior space of the processing tower 103. A circulating passageway 105 is provided in such a way that one end thereof is connected with a lower sidewall of the processing tower 103, while the other end thereof is connected with the spray member 104. A first pump 106 is provided at a midway of the circulating passageway 105 which is located in the vicinity of an exhaust gas-processing water discharge port of the processing tower 103. A heat exchanger 107 for cooling the exhaust gas-processing water is provided at a midway of the circulating passageway 105.
A cooling tower 109 provided at an upper portion thereof with a fan 108 for generating the cooling water by taking advantage of the evaporation heat of water is disposed next to the exhaust gas-processing tower 103. A spray member 110 for spraying cooled water is provided at an upper portion of the interior space of the cooling tower 109. A cooling water-circulating passageway 111 is provided in such a way that one end thereof is connected with a lower sidewall of the cooling tower 109, while the other end thereof is connected via the heat exchanger 107 with the cooling water spray member 110. The cooling water-circulating passageway 111 is designed to circulate cooling water from a lower sidewall of the cooling tower 109 via the heat exchanger 107 to the cooling water spray member 110.
A second pump 112 is provided at a midway of the cooling water-circulating passageway 111 which is located in the vicinity of the cooling tower 109. A make-up passageway 113 is connected with a lower sidewall of the cooling tower 109 so as to supply water from outside the system to the bottom portion of the cooling tower 109. A blow-down passageway 114 is connected with the bottom of the cooling tower 109, thereby allowing water to be continuously or periodically discharged from the bottom portion of the cooling tower 109.
According to this conventional exhaust gas cooling system, an exhaust gas containing water, for example an exhaust gas generated through the combustion of hydrocarbon, is introduced from the inlet port 101 into the exhaust gas-processing tower 103. The first pump 106 is actuated so as to supply an exhaust gas-processing water from the bottom portion of the exhaust gas-processing tower 103 via the circulating passageway 105 to the heat exchanger 107. On this occasion, as the second pump 112 is actuated, the cooling water of the bottom of the cooling tower 109 is supplied via the cooling water-circulating passageway 111 to the heat exchanger 107.
As a result, the exhaust gas-processing water is cooled down, and the resultant cool water is supplied via the circulating passageway 105 to the spray member 104. The cooled water is then ejected from the spray member 104 into the space inside the exhaust gas-processing tower 103 so as to cool the exhaust gas that has been introduced into the exhaust gas-processing tower 103. The exhaust gas thus cooled is then transferred via the exhaust gas outlet pipe 102 to the absorption tower for carbon dioxide for example. On the other hand, the cooling water whose temperature has been raised at the heat exchanger 107 through the heat exchange thereof with the exhaust gas-processing water is fed via the cooling water-circulating passageway 111 to the cooling water spray member 110 of the cooling tower 109.
The cooling water thus warmed is then ejected from the spray member 110 into the space inside the cooling tower 109 and by the actuation of the fan 108, is cooled due to the evaporation heat to be generated through the evaporation of water accumulated at the bottom of the cooling tower 109. This cooling water is then accumulated at the bottom portion of the cooling tower 109. The water inside the cooling tower 109 is consumed through the evaporation thereof. In order to compensate this consumption of water, water (make-up water) is supplied from outside the system to the cooling tower 109 through make-up passageway 113.
According to the aforementioned exhaust gas cooling system however, when an exhaust gas containing moisture (for example, an exhaust gas to be generated from the combustion of hydrocarbon) is introduced into the exhaust gas-processing tower 103 and then, cooled water is ejected through the spray member 104 disposed at an upper portion of the exhaust gas-processing tower 103, the water included in the exhaust gas is caused to condense and stored, as a condensate, at the bottom portion of the exhaust gas-processing tower 103. Since the volume of exhaust gas-processing water is caused to substantially increase due to the generation of this condensed water, part of exhaust gas-processing water is required to be discharged outside the system from the bottom of the exhaust gas-processing tower 103 via a discharge passageway 115. As a result, the load for processing waste water is caused to increase, thus raising a problem.
Furthermore, since the water circulating through the cooling water-circulating passageway 111 is cooled by taking advantage of the evaporation of water at the water inside the cooling tower 109, it is required to supply water from outside the system to the cooling tower 109 through make-up passageway 113. Since this external water contains salts such as calcium, etc., the salts are also caused to concentrate in the circulation process in the cooling water-circulating passageway 111. As a result, the water containing a concentration of salts is required to be frequently discharged outside the system from the bottom of the cooling tower 109 via the blow-down passageway 114.
Therefore, an object of this invention is to provide an exhaust gas cooling system wherein a portion of exhaust gas-processing water incorporating therein the condensed water that has been generated through the condensation of moisture included in the exhaust gas at the exhaust gas-processing tower is introduced as a make-up water into a cooling tower, thereby making it possible to minimize the load for processing waste water, to decrease the quantity of water to be supplied to the cooling tower, and to minimize the frequency of the blow-down from the cooling tower.
Another object of this invention is to provide an exhaust gas cooling system which is capable of omitting the provision of a heat exchanger, of reducing the manufacturing cost of the system, of miniaturizing the cooling tower, and of reducing the capacity thereof.
Namely, this invention provides an exhaust gas cooling system comprising;
an exhaust gas-processing tower provided at a lower portion with an inlet port for an exhaust gas containing moisture and also provided at an upper interior space with a spray member;
a circulating passageway for circulating an exhaust gas-processing water from a bottom portion of the exhaust gas-processing tower to the spray member;
a heat exchanger provided at a portion of the circulating passageway for cooling the exhaust gas-processing water;
a cooling tower for generating the cooling water by taking advantage of the evaporation heat of water, thereby allowing the cooling water to circulate passing through the heat exchanger; and
a water supply passageway for supplying the exhaust gas-processing water passing through the circulating passageway to the cooling tower as a portion of make-up water.
According to this invention, there is also provided an exhaust gas cooling system comprising;
an exhaust gas-processing tower provided at a lower portion with an inlet port for an exhaust gas containing moisture and also provided at an upper interior space with a spray member; and
a cooling tower for cooling an exhaust gas-processing water existing at a bottom portion of the exhaust gas-processing tower by taking advantage of the evaporation heat of water, thereby allowing the water thus cooled to be fed to a spray member of the exhaust gas-processing tower.
In the exhaust gas cooling system of this invention, the exhaust gas-processing tower may be constructed such that it is provided with an exhaust gas outlet pipe which is connected with a carbon dioxide absorption tower.
The exhaust gas cooling system of this invention may further comprise an air cooler which is provided at a portion of a passageway located between the exhaust gas-processing water outlet port of the exhaust gas-processing tower and the cooling tower.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.